ICD-10 Code T31.91: 90%+ TBSA, 10-19% third-degree burns

Key takeaways

ICD-10 Code T31.91 covers burns involving 90% or more of body surface, with third-degree burns across 10-19% of body surface.

Category T31 classifies thermal burns only. Chemical injuries belong to the parallel corrosion category T32, so T32.91 is a different code.

The fifth character measures third-degree burns as a share of the whole body, not as a share of the burned area.

T31.91 is an extent code. Report it alongside site-specific burn codes from T20-T25 rather than on its own.

Practice management software like Pabau helps burn teams record TBSA, burn depth, and site at the point of care.

ICD-10 Code T31.91 is a billable code for burns involving 90% or more of body surface, with third-degree burns covering 10-19% of body surface. It records burn extent, so it travels with the site-specific codes that say where the burns are.

The code turns on two separate percentages rather than one. Accordingly, this reference covers the official description, code structure, TBSA calculation, sequencing rules, documentation requirements, and billing validity.

ICD-10 Code T31.91: official description and billable status

T31.91 is a billable, specific ICD-10-CM code valid for HIPAA-covered transactions. It sits in category T31, Burns classified according to extent of body surface involved. Specifically, its official descriptor is Burns involving 90% or more of body surface with 10-19% third degree burns.

Category T31 covers thermal burns. Because definitions can shift with each annual update, confirm the descriptor and the current edition year against the CDC/NCHS ICD-10-CM web tool, which carries the authoritative US tabular list.

What T31.91 means: decoding the code structure

Every character in T31.91 carries a defined meaning, so misreading one position produces a different code and a different picture of the injury.

• T – Chapter 19 of ICD-10-CM, which covers injury, poisoning, and other consequences of external causes
• 31 – the category for burns classified by extent of body surface, as opposed to T20-T25, which identify the burn site
• .9 – fourth character: total body surface area burned is 90% or more
• 1 – fifth character: third-degree burns cover 10-19% of body surface

Both digits are measured against the same denominator. Each one describes a share of the whole body, so the third-degree figure can never exceed the total burn figure.

That single constraint shapes the entire category, and it is the fastest way to sanity-check a T31 code. Subcategory T31.1 has only two children, because a 10-19% burn cannot carry more than 19% full-thickness involvement. T31.9 is the only subcategory with all ten children, since a body burned to 90% or more can carry any third-degree share at all.

For example, a record showing 95% TBSA burned, with 15% of body surface at full thickness, maps to T31.91. Now move the third-degree figure to 22% and the correct code becomes T31.92.

The T31.9 subcategory: burn extent codes at 90% and above

Subcategory T31.9 covers burns involving 90% or more of body surface. The fifth character then records how much of the body reached third degree, in ten-point bands. The table below lists all ten codes.

T31.90 is easy to misread. It is not a placeholder for an undocumented percentage. Instead, it is the specific band for third-degree burns covering 0% to 9% of body surface. Use it only when the record supports that range.

Choosing T31.91 over T31.90 records that at least a tenth of the whole body reached full thickness. Registries and payers read that difference, so the fifth character deserves the same scrutiny as the fourth.

T31 versus T32: burns and corrosions are different categories

T31 and T32 are structurally identical, which is exactly why they get confused. T31 covers burns from thermal sources such as fire, heat, hot liquids, radiation, electricity, and friction.

T32 covers corrosions, meaning chemical injuries. Its subcategories mirror T31 band for band, down to codes such as T32.84. T32.91 sets the same two extent thresholds as T31.91, so the mechanism of injury decides which category applies.

Confirm the mechanism in the clinical notes before you pick a category. A chemical exposure coded to T31 misstates the injury, and it feeds the wrong figure into every burn registry that draws on the record. A corrosion also needs a code from T51-T65 to identify the chemical and the intent, such as T56.7X4A.

How to calculate TBSA using the rule of nines

The rule of nines is the standard bedside method for estimating total body surface area burned in adults. It assigns a fixed percentage to each major body region so clinicians can tally coverage quickly.

Reaching 90% TBSA means nearly every region on that list is involved. Notably, the American Burn Association treats burns at or above 20% TBSA as major burns, so a patient in the T31.9 band sits far beyond the threshold for transfer to a verified burn center.

The Lund-Browder chart is more accurate for children, because it adjusts head and limb percentages by age. Either method, however, is clinically acceptable. The method used should be named in the note, which is easier when clinical measurement tracking is built into the burn assessment template.

Coding and sequencing rules for T31.91

Burn sequencing sits in Section I.C.19.d of the ICD-10-CM Official Guidelines for Coding and Reporting, in the subsection on burns and corrosions classified by extent of body surface involved. The guidelines direct coders to assign a T31 code when the burn site is not specified, or when additional data is needed. Two further uses are advisable rather than required.

• It is advisable to add a T31 code when burn units need data for evaluating mortality.
• It is also advisable when a third-degree burn involves 20% or more of body surface.

Advisable is not mandatory: the 20% figure is a threshold tied to third-degree extent, not a rule that every third-degree burn triggers an extent code. T31.91 sits under that threshold, since its third-degree band tops out at 19% — it is reported for the extent data itself, not the 20% advisory.

In practice T31.91 is an additional code. The burn-site-unspecified case that would make a T31 code primary is uncommon at this severity, since charts for a 90% burn almost always name the regions involved.

• Multiple burn sites: sequence the burn of the highest degree first, then report T31.91 to capture overall extent.
• Seventh characters: site-specific codes from T20-T25 need A, D, or S for the encounter type. T31.91 takes no seventh character.
• Non-healing burns: code as an acute burn, and code necrosis of burned skin as a non-healed burn. Graft complications carry their own codes, such as T86.828.
• External cause codes: also add the code that identifies how the burn happened, alongside place, activity, and status codes where the record supports them.

For reference, the CMS ICD-10 codes page publishes the guidelines and tabular files for each fiscal year.

The same sequencing logic applies to neighboring extent codes such as T31.52 and T31.32.

Codes reported alongside T31.91

In fact, T31.91 is rarely the only code on a burn claim. The table below shows the code families that usually travel with it.

Teams that route burn charts through claims management software can hold these encounters for a sequencing review before anything is billed.

Documentation requirements for assigning T31.91

T31.91 cannot be assigned from a record that documents only the burn site and depth. Five elements need to be explicit before a coder can apply it with confidence.

• Total TBSA burned: a numeric percentage of 90% or above, with the assessment method named. Narrative phrases such as extensive or most of the body do not map to a code.
• Third-degree extent: a separate numeric percentage of body surface at full thickness, falling between 10% and 19%.
• Mechanism of injury: a thermal source, confirmed in the notes, so the case is not coded to the T32 corrosion category by mistake.
• Burn sites: each region involved, documented individually, to support the companion T20-T25 codes.
• Depth by region: which regions are first, second, and third degree, so the 10-19% figure can be reconstructed from the record.

When the chart carries a TBSA figure but no depth breakdown, query the attending physician before assigning T31.91. Otherwise, picking a fifth character without documented support is a compliance risk on a high-cost inpatient stay.

Digital intake forms can prompt for each element at the point of care. That is far cheaper than reconstructing a TBSA calculation weeks after discharge.

Retaining the burn assessment worksheet, or its electronic equivalent, matters as much as the percentages themselves, because payers auditing high-cost burn stays ask for it specifically. In short, meeting healthcare compliance requirements for burn records means keeping that worksheet attached to the chart.

Common coding errors with T31.91

Burn coding at this extent is high-stakes, and these are the errors worth checking before submission.

• Coding a chemical injury to T31: corrosions belong to category T32 instead. A chemical injury at this extent is T32.91, not T31.91.
• Reading the fifth character as a share of the burned area: the 10-19% figure is a share of the whole body surface. That is why it can never exceed the fourth character band.
• Treating T31.90 as unspecified: T31.90 is the documented 0% to 9% band. In other words, it is not the code for a record that never states a third-degree figure.
• Dropping the site-specific codes: T31.91 supplements T20-T25 codes and never replaces them. Indeed, on its own it says nothing about where the burns are.
• Calling the extent code mandatory: the guideline wording is advisable, not required. It is tied to a 20% third-degree threshold rather than to any documented third-degree burn.
• Skipping the annual validity check: confirm the code and its descriptor against the current tabular list each fiscal year before it goes on a claim.

A compliance management workflow that includes a burn coding checklist catches most of these before submission. Many facilities add a burn audit to their quarterly review for exactly that reason.

Clinical context: who is coded with T31.91?

Burns covering 90% or more of body surface are rare and almost always catastrophic. Even so, T31.91 shows up in a small set of predictable settings.

• Burn center admissions: typically, patients at this extent are admitted to a verified burn center, and carry site-specific codes across most body regions.
• Fluid resuscitation: the Parkland formula uses TBSA to set initial intravenous fluid volumes. The percentage behind T31.91 is a clinical figure first and a coding figure second.
• Grafting and reconstruction: 10-19% full-thickness involvement means surgical debridement and skin grafting. Accordingly, teams running plastic surgery EMR software track those procedures against the underlying diagnosis.
• Transfer cases: a community hospital may assign T31.91 before transfer. The receiving burn center needs the same percentages to code the stay consistently.
• Rehabilitation and follow-up: survivors need months of wound care and therapy. Those encounters take seventh character D on the site-specific codes, which physical therapy EMR software can carry forward from the acute record.

Code validity: is ICD-10 Code T31.91 billable?

T31.91 has been part of ICD-10-CM since the code set took effect on October 1, 2015. It remains valid and billable in the FY2026 edition, which took effect on October 1, 2025, with no revision to its descriptor or structure.

Confirm validity for each coding period against the official tabular list. ICD-10-CM is maintained by the National Center for Health Statistics at the CDC. In addition, the Official Guidelines are approved jointly by CMS, NCHS, the American Hospital Association, and AHIMA. By contrast, the WHO version of ICD-10 is the international reference and does not govern US billing.

The AAPC ICD-10-CM code lookup is a quick way to cross-check T31.91 against its neighbors.

Neighboring bands such as T31.85 and T31.11 deserve the same annual check.

How Pabau supports burn care documentation and coding

Burn teams working at T31.91 severity track a total TBSA figure and a separate third-degree figure. They also track a site-specific code for nearly every region of the body. When those numbers live only in free-text notes, coders spend their day chasing them instead of coding.

Pabau, a practice management and EMR platform, lets burn services build structured encounter templates in their clinical forms. Each template can prompt for total TBSA, third-degree extent, assessment method, and site, and flag any field left empty before the note is finalized.

Everything then sits in one patient record, alongside the burn assessment worksheet and the operative notes for grafting. As a result, coders open a chart that already answers the questions T31.91 depends on.

The outcome is fewer coder queries, faster code assignment, and documentation that stands up when a payer audits a high-cost burn stay months later.

Keep burn care documentation in one place

Pabau helps burn and plastic surgery teams capture TBSA, burn depth, and site at the point of care. Coders get what they need to assign T31.91 accurately.

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Conclusion

T31.91 only holds up when the record proves two separate numbers. Total burn extent has to reach 90% of body surface, and third-degree burns have to cover 10-19% of body surface.

Two checks stop most errors in this family. Confirm the injury was thermal rather than chemical, because a corrosion belongs to T32. Then confirm the third-degree figure is measured against the whole body, not against the burned area.

A burn assessment template with separate fields for total TBSA and third-degree extent fixes both at the source. The fifth character then reflects what a clinician actually documented, rather than whichever band a coder can defend.

Pabau keeps those fields, the burn worksheet, and the operative record in one chart. To see how it fits your burn unit’s documentation workflow, book a demo.

Continue your research

Need the next band up in the same subcategory? ICD-10 Code T31.94 covers burns over 90% of body surface with 40-49% third-degree involvement.

Estimating TBSA at the bedside? Body burn percentage chart walks through rule of nines estimation for adult burn patients.

Coding a smaller burn? ICD-10 Code T31.42 covers burns involving 40-49% of body surface, under the same sequencing rules.

Billing the procedures that follow a burn diagnosis? CPT Code 11044 covers bone debridement, which can accompany severe full-thickness burns.

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